In producing hydrocarbons or the like from loosely or unconsolidated and/or fractured subterranean formations, it is not uncommon to produce large volumes of particulate material (e.g. sand) along with the formation fluids. These particulates routinely cause a variety of problems which result in added expense and substantial downtime. For example, in most instances, particulates in the produced fluids cause (1) severe erosion of the well tubing and other production equipment; (2) partial or complete clogging of the flow from the well which requires workover of the well; (3) caving in the formation and collapse of the well casing; (4) extra processing of the fluids at the surface to remove the particulates; and (5) extra cost in disposing of the particulates once they have been separated. Accordingly, it is extremely important to control the production of particulates in most operations.
One widely used technique for controlling the production of particulates (e.g. sand) from a well is that which is known as "gravel packing". In a typical gravel pack completion, a screen is lowered into the wellbore and positioned adjacent the interval of the well which is to be completed. Particulate material, collectively referred to as gravel, is then pumped as a slurry down the well and into the annulus which is formed between the screen and the well casing or open hole, as the case may be, to deposit the gravel around the screen. The gravel is sized so that it forms a permeable mass which allows fluid flow into the screen while blocking the flow of any particulates produced with the fluids. While gravel packing is well established for completing loose, sand-producing formations, its cost in both new completions or workovers is substantial which may seriously effect the overall economics of a well.
Another usually less expensive technique for controlling sand production from a formation involves the injection of a consolidating agent or solution into the pore space of the formation at and near the wellbore. Examples of such consolidating agents include plastics such as phenolformaldehyde, furan resins, and epoxy resins.
The consolidating agent is flowed down the wellbore and is forced under pressure into the formation where it normally penetrates for a distance of several inches to several feet where it occupies the pore spaces and envelopes the sand grains of the formation. Under the influence of the elevated temperature in the formation, after a few hours, the agent polymerizes and hardens. As it does so, it shrinks to about one-half to about One-third of its original liquid volume, leaving much of the pore space in the treated area or zone of the formation open for fluid flow. At the same time, the consolidating agent coats the sand grains and cements them together into a consolidated, permeable mass.
While the treated or consolidated zone of the formation will lose some permeability, there is normally sufficient permeability left in the consolidated sand mass to allow adequate flow of fluids therethrough. The consolidating agent used must be one which is chemically inert and permanent in nature after the agent becomes solidified in that it must be substantially unaffected by subsequent contact with any of the formation fluids, e.g. oil, gas, and/or water. Consolidating agents of this type must have a sufficiently low initial viscosity to allow it to freely enter the near-wellbore formation. Further, the agent must set within a reasonable time at the temperature of the formation to be consolidated.
In some instances, a "wetting" agent may be added to the consolidating solution to assist in displacing oil and water from the sand grains to insure a good bond between the consolidated solution and the sand grains. Also, an accelerator or the like can be added to the solution or pumped separately into the wellbore to adjust the setting time of the consolidating solution. Sand grains cemented together with a good consolidating agent forms a rock matrix that is firm and hard and nearly as strong in its resistance to compressive forces as natural sandstone, in which the sand grains are cemented by siliceous or calcareous materials.
The present invention provides a method using still another consolidating agent which is capable of being placed into the pore space of a near-wellbore zone of a subterranean formation and which will, when allowed to set at the elevated temperature of the formation, will harden or solidify to produce a strongly-bonded, permeable rock-like matrix which is substantially unaffected by the formation fluids, thereby controlling the production of sand grains from the treated zones.